August 18th, 2012

Thick Cortex Offers Clue to Better Memory

Reviewed by Zalman S. Agus, MD; Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner

Action Points
-- This study looked to identify individuals over the age of 80 who seemed immune
to age-related memory impairment, and determine if they were also resistant to
age-related loss of cortical brain volume.
-- Note that the study found that aged individuals without cognitive impairment
had cerebral cortex which was significantly thicker than their healthy age
matched peers and displayed no atrophy compared to a 50- to 65-year-old healthy
group.

Sharp minds in old age correlated with significantly thicker cortical layers in an area of the brain associated with memory and cognitive performance, investigators reported.

Brain scans of "SuperAgers" (those ages ≥80 with above-average cognitive function) revealed a significantly thicker cerebral cortex and left anterior cingulate cortex, as compared with an age-matched control group. In fact, cortical volume did not differ from that of normal middle-aged adults, as reported online in the Journal of the International Neuropsychological Society.

The SuperAgers performed significantly better than the age-matched control group on a standardized test of memory and at least as well as the middle-age control group, according to Emily Rogalski, PhD, of Northwestern University in Chicago, and co-authors.

"The findings show that memory decline isn't the only route for the aging brain," Rogalski said. "It seems there are some unique biologic factors that contribute to super aging, and we looked at one example, the cortex of the brain. There's a lot more to look at."

Whether SuperAgers were born with greater cortical volume or resisted age-related cortical atrophy is unclear, she added.

Norms for cognitive function decline with age, such that "normal" for an 80-year-old person is usually markedly lower than the norm for a 50-year-old, particularly on tests of episodic memory. Whether that decline is an inevitability of aging remains unclear, the authors wrote in their introduction.

The age-related decline in cognitive function has outliers, people who retain good memory performance beyond 80. The observation has led to speculation about the existence of an inherent "alternative trajectory" that resists neuroanatomical changes and decline in cognitive function observed in older people.

To investigate potential neuroanatomical and morphologic characteristics associated with well-preserved memory in SuperAgers, Rogalski and colleagues studied 12 healthy individuals ages ≥80 with above-average memory performance. Investigators also recruited an age-matched control group (N=10) and a group of healthy middle age adults (50 to 65, N=14).

All of the participants scored within one standard deviation of the average range for memory performance for their age group, a finding which confirmed that none was cognitively impaired. They also underwent a standardized T1-weighted three-dimensional MRI brain scan.

The two older groups did not differ significantly with respect to mean age (~83), and the three groups had similar education levels. Overall, the SuperAgers demonstrated episodic memory performance at least as good as that of the middle-age group, and significantly better than that of the older control group (P<0.001).

The SuperAgers also did not differ from the middle-age control group with respect to nonmemory cognitive function.

With regard to MRI findings, the older control group exhibited significant cortical atrophy in multiple regions compared with the middle-age controls. The pattern of atrophy was consistent with what has been observed in previous studies, the authors wrote. The older individuals had a mean normalized cortical volume of 244.13 versus 306.43 mm3 in the middle-age control group (P<0.001).

Brain scans showed no significant cortical atrophy in the SuperAgers, whose mean cortical volume did not differ significantly from the middle-age control group (288.05 versus 306.43 mm3, P=0.08). Moreover, an area of the left anterior cingulate was thicker in the SuperAgers than in the control group.

The SuperAgers' mean cortical volume also differed significantly from that of the older control group (P<0.001).

Correlational analysis showed a significant positive association between memory performance and mean cortical volume across the three groups (r=0.532, P=0.001).

Although increased cingulate cortical thickness did not correlate with memory performance, the authors noted that previous studies have suggested that normal cingulate function plays a role in maintaining the integrity of multiple cognitive domains.

Investigators have found no common environmental factors to explain the cortical thickening. Some patients smoked, others didn't. Some regularly consumed alcohol, others never drank. Some exercised regularly, some never exercised. Some were financially secure, and others had struggled financially throughout their lives.

"We can't say eat a cup of blueberries or drink a glass of wine and you'll have better memory," said Rogalski.

Investigators also have yet to analyze data on mind-stimulating activities that might account for differences in memory, such as reading or playing chess.

The ongoing program has increased its SuperAger population to 30 and will follow all participants at 18-month intervals. Additionally, some participants have agreed to donate their brain for study after they die.

The study was supported by the Davee Foundation, Northwestern University, and the National Institutes of Health.